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چکیده
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This study numerically investigates the effects of different riverbed forms (flat, ripple, and dune) on pollutant dispersion in open channels using the Flow-3D model and computational fluid dynamics (CFD). The numerical simulations were operated using the Reynolds-averaged Navier-Stokes (RANS) equations which was coupled with an advection-dispersion model for three distinct bed forms. Sodium chloride is used as a tracer material to track pollutant transport. The results reveal that bed forms profoundly influence pollutant dispersion rates in open channels. Ripple beds exhibited the fastest dispersion due to enhanced turbulence and mixing, promoting the breakdown and transport of pollutant particles throughout the water column. In contrast, flat beds displayed the slowest dispersion owing to minimal turbulence and mixing, resulting in higher pollutant concentrations near the source. Dune beds exhibited intermediate dispersion rates compared to ripple and flat beds, with complex flow patterns inducing both turbulence and stratification, leading to variations in dispersion based on flow conditions and pollutant properties. In addition, flow characteristics like velocity, and surface roughness played crucial roles, with higher velocities and rougher beds generally promoting faster dispersion through increased turbulence and mixing. However, excessively high velocities could also hinder dispersion by forming flow separation zones that trap pollutants.
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